Conventionally, positioners for controlling the openings of valves have been, for example, positioners wherein the critical components have been configured as illustrated in FIG. 10, for example. See, for example, Japanese Unexamined Patent Application Publication No. 2012-207756. In this figure, 100 is a higher-level device, 200 (200A) is a positioner, and 300 is a regulator valve.
The positioner 200A is provided with a control calculating portion 1, an electropneumatic converting portion 2, a pneumatic circuit portion 3, and a valve opening detector (valve opening detecting portion) 4, assembled together with a valve 300. In the below, this positioner 200A will be termed a “single-unit positioner.”
In this single-unit positioner 200A, the valve opening detector 4 detects the current degree of opening of the valve 300, and sends it as an actual opening signal Xpv to the control calculating portion 1. The control calculating portion 1 uses, as inputs, the opening setting signal Xsp for the valve 300, sent from the higher-level device, and the actual opening signal Xpv, from the valve opening detector 4, to calculate the difference between the opening setting signal Xsp and the actual opening signal Xpv, and generates, and sends to the electropneumatic controlling portion 2, a PWM signal (a pulse width modulation signal), obtained through performing PID control calculations on this difference, as a control signal MV.
The electropneumatic converting portion 2 converts into an air pressure (a nozzle back pressure) Pn the control signal MV from the control calculating portion 1. The pneumatic circuit portion 3 uses the pneumatic signal Pn from the electropneumatic converting portion 2 as an input air pressure and amplifies this input air pressure Pn to produce an output air pressure Po, and outputs it to the operating device (not shown) of the valve 300. Doing so causes the air of the air pressure Po to flow into a diaphragm chamber within the operating device, to adjust the opening of the valve 300.
Note that the control calculating portion 1 is provided with a function for performing diagnostics on the valve 300, based on the changes in the control state, for sending the diagnostic results to the higher-level device 100, etc.
In this single-unit positioner 200A a control calculating portion 1, an electropneumatic converting portion 2, a pneumatic circuit portion 3, and a valve opening detector (valve opening detecting portion) 4 are contained within a single case 10, and this case 10 is assembled together with a valve 300. Because of this, there is a difficulty in that there is a susceptibility to the effects of vibrations of the valve 300 and a sensitivity to the temperature of the fluid that flows through the valve 300.
Given this, in order to reduce the susceptibility to the effects of vibration and temperature, a positioner 200 (200B), as illustrated in FIG. 11, is proposed wherein the case 10 is divided into a first case 10-1 and a second case 10-2, wherein the valve opening detector 4 is contained within the first case 10-1, and assembled together with the valve 300, where the control calculating portion 1, the electropneumatic converting portion 2, and the pneumatic circuit portion 3 are contained within the second case 10-2 and disposed at a location that is away from the valve 300. See, for example, Japanese Design Registration No. 1128492. In the below, this positioner 200B will be termed a “separated-type positioner.”
Note that the actual opening signal Xpv from the valve opening detector 4, contained within the first case 10-1, are sent to the control calculating portion 1 through the provision of a terminal block 5 in the second case 10-2, where this terminal block 5 and the valve opening detector 4 are connected through a cable 6.
However, in this separated-type positioner 200B, the actual opening signal Xpv (which is a weak analog current signal) from the valve opening detector 4 is susceptible to the effects of noise due to the cable 6 that extends between the valve opening detector 4 and the control calculating portion 1. This causes problems such as the following to occur.
(1) The effects on control are large due to performing control calculations using the actual opening signal Xpv, which is susceptible to the effects of noise.
(2) It is necessary to test the noise at the terminal because the control calculating portion 1 is connected to the valve opening detector 4 by the cable 6 through the terminal block 5. Additionally, performing surge protection, and the like, at the terminal requires the positioner to be larger. There is also the possibility that the signal itself will be affected through the additional components after surge protection.
(3) Noise testing must be performed on the signal line for the actual opening signal Xpv, which transmits minute changes.
(4) Because the valve opening detector 4 is separated from the control calculating portion 1, temperature correction on the valve opening detector 4 is difficult.
(5) While there is no need for an anti-explosive structure in the second case 10-2 if it is placed in a safety zone, doing so requires the cable 6 between the valve opening detector 4 and the terminal block 5 to be longer, increasing the effects of noise on the actual opening signal Xpv.
The present invention was created to solve such a problem, and an aspect thereof is to provide a positioner that is robust to the effects of noise.